Variable pitch propeller



Oct. 9, 1951 P. J. QUINN VARIABLE PITCH PROPELLER 3 Sheets-Sheet 1 FiledApril 29, 1948 m m w.

El!!! .7. Quin/Z B W ATTORNEY Oct. 9, 1951 P. J. QUINN VARIABLE PITCHPROPELLER 5 Sheets-Sheet 2 Filed April 29, 1948 INVENTOR.

A T TO RNEY Oct. 9, 1951 Filed April 29, 1948 .Uz're can P. J. QUINNVARIABLE PITCH PROPELLER 3 Sheets-Sheet 5 INVENTOR.

ATTORNEY Patented Oct. 9, 1951 UNITED STATES- "PATENT OFFICE VARIABLEPITCH PROHE-LLER mu. Quinn; South OrangeQN. J. Application Apr-H 29,194s, SeriaINo. 23,9109 I This invention relates to variable pitchpropelfor aircraft and more particularly to variable pitch propellersemploying aerodynamic and cen- 'tnifugal forces for automaticallycontrolling the pitch. The application for patent herein com prises {acontinuation-in-part of application .Serial No. 705,971, filed October26-, 19 46; which has become abandoned.

Variable pitch propellers have been proposed in which the aerodynamicforces and centrifugal .force are utilized to maintain or effect changesin pitch in response to propeller rotational speed and airstre'amvelocity. Such prior propellers :operate in response to relatively smallturning forces-and against relatively high-frictional resistance toturning, with the inherent result that such propellers have not had thedesired sensitivity and stability, both being important (and basicrequirements for satisfactory operation.

Accordingly, an object of the present invention is to provide anautomatic variable pitch :propel its in which the aerodynamic forcesemployed tor effecting pitch changesor for maintaining a desired pitchare relatively high and inwhich the individual :blades are retained uponanti friotion :beesrings offering low resistance to turning in responseto the forces present.

Another object of the invention is the provision -fo an automaticvariable pitch propeller operated by centrifugal and aerodynamic forcesin which blade oifset "is relatively small and in which the :bladecenter of gravity is readily maintained well within the area encompassed-by the blade retention bearings.

A further obiect -'of the invention to providean automatic variablepitch propeller in which the blade bending moments are minimized and inwhich the forces tending to hold the propeller blade in any pitchposition within the operating range are of substantially equalmagnitude.

.Still another object of "the invention is the provision of a propellerof the typedescribed which the blades extend mor closely radially efwtherotation axis andin which adequate aerodynamic and centrifugal turning:momcntsand stability are nevertheless :attained- )SJS well :as en-Amnced. I

A .further object of the invention is to provide a variable pitch bladeretention in which the blade axis extends at an angle to thevaxis ofpitch u'otation'of the blade with respect :to its .hub, and :in whichthe-pitchrotation axis is inclined to'the normal-in order :to increasertheeif-ectiveness- -of the aerodynamic forces within the normal range40% gp'itch variation.

2 ohms. (o1. go-1505p (A further .obiect. of the invention is theprovision of an automatic variable pitch propeller rin. whichfeathering. of the propeller may occur when propeller .rotationisstopped, and in which the (degree of feathering -may be readilycontrolled to provide .or. retain a sufficient turning :moment tore-establish. rotation.

The .above and other novel features of the invention will appear morefully. hereinafter from the following detailed description when taken inconjunction with. the accompanying drawings. It is expressly understood,however, that the sdrawi-ngsiare employed ,for purposes of illustration:only --and are not designed as a definition of thell imitation of theinvention, reference being bad .tottheappended. claims for this purpose.

In the drawingswherein like reference. characters. indicate like parts:Fig. l is a side .eleyationof a three blade pro.- rpeller hub havingblade shanks extending there- .from accordance with the invention;

Fig. 2 is a: front elevation of. the propeller :shown inwFig. 1-.;.. vFig-3. is subst tially an axial section taken through the socket .of oneof the blades of Figs. .1 :and 2, the section extending through theinter- :section of the retention bearing and blade neutrol -axes thereshown;

Fig.4 is a transverse section taken substantially on the line Arr-Q ofFig. 3, bent at e and fol lowing the plane of rotation in part and theretention bearing axis in part, the blade shank and retention collarelement being shown in elevation; and.

Fig. .5 is a three dimension diagram of a propeller and bladeillustrating generally the forces and couples actin iunder normal flightconditions at .a- .point approximately three-quarters of the Joladerddiusfrom the hub.

Referring to .Figs. 1 through 4, there is shown ra propeller hub (I).having blades L2 retained therein :and driven by an engine shaft Mproiecting from-an engine nose, housing or fuselage such as Hi. The hubi0 is provided with a plurality of tubular blade" sockets 18 extendingto a substantial degree radially of the hub but inclined at an angle tothe normal as will be more v.f-ull-y explained.- Each of the bladesockets is provided Withga plurality of retention thrust bearings ZOwhich bear against retention nuts 22 internally threaded, within the endof each socket. Illhe retention thrust bearings 29 support within.eachsocket, a split blade holding collar com- :posed of parts .24 and126, having a cylindrical thrust bearing receiving surface .28 and ashoul- 3 der 30 against which the thrust bearings 20 bear.

A bearing 32 opposing the retention bearings 20 is provided between thesplit collar and the socket near the base thereof in order to slightlypreload the bearings 20 and hold the blade in proper position when notrotating. The retention thrust bearing 20 and pre-load bearing 32 areclamped in position within the socket against a. shoulder 34. Theinternal race 35 of the bearing 32 may be split to facilitate itpositioning Within a channel 36 provided therefor in the shoulder 30 ofthe split collar. The retention nut 22 may be securly locked in positionby" means of a ring 38 secured to the nut 22 by. screws y it, the ringhaving lugs 42 engaging slots 44 herein assumed to be at about radius.

The forces available to effect pitch changes in a propeller of the typethus far described are (1) those components of centrifugal force whichact upon the blade in a direction normal to the blade axis and whichtend to pull it into the plane of rotation such as YZ (Fig. 5) passingthrough the blade mounting point e. and which are utilized to increasepropeller pitch, and (2), thrust and torque forces,generally alluded toas aerodynamic forces, tending to drag the blade rotationally behind anormal to the propeller shaft passing .75 of the blade through the blademounting point and tending to formed by the castellated end of eachsocket.

The split collar members 24 and 26 are provided with a suitable bladeshank receiving recess and are adapted to be snugly clamped about theshank of the blades I 2 by means of recessed clamp bolts .48.

Journalled within the hub and co-axial with :the axis of hub rotation isa bevel gear 50 sup- .ported on a bearing 52.

A sector bevel gear 54, provided upon the collar members 24 and 26 ineach of the sockets, meshes with the co-axial gear 50, in order tosynchronize the movements of all blades and pool the turning moments,although it will readily appear that if all blades and their retentionsare exactly alike, the need for such synchronizing gear may beeliminated.

The hub is splined upcn the engine drive shaft j H and the cavity inwhich the bevel gears are positioned isadapted to be supplied withlubricant, which is prevented from escaping through the blade sockets bymeans of a ring seal 56 held in position by a flange on the retainingnut 22,

' the split collar and retention nut.

- It will be observed in Fig.5.: and 4 that the split collars securingthe shank of the blades l2 therewithin, support each of the blades withthe blade axis extending at an angle to the axis of the retentionbearing contained within each hub socket. The blade axis is positionedat an angle 6' :to the retention bearing axis and lies rearwardly of andtrails the bearing axis, it being assumed that the flight direction ofthe propeller is in the direction of arrow A in Fig. 3, and thedirection of rotation of the hub is indicated by the arrow .B in Fig. 4.The blade neutral axis and retention bearingaxis converge at a pointindicated at e,

'which point is located at a distance from the shaft axis as may bedetermined in any particular v design. The plane of rotation indicatedin Fig. 3

is taken so as to pass through the point e and will hereinafter bereferred to as the plane of rotation. The axis of the retention bearingis inclined forwardly of the plane of rotation by an angle Q5): and

1 also in advance of the direction of rotation by an angle 45v, thusforming a total angle between a radial lying in the plane of rotationand extending through the point e, and the thrust bearing axis.

Since the axis of rotation of each split collar is the retention bearingaxis and is askew to the propeller shaft axis, the bevel gear 50 andmating gears 54 are suitably cut for skew gear engagement. In order toneutralize the efiect of the centrifugal twisting moment of each blade,there the plane XY' or l2,is at H.

of the blade neutral axis 14 with the plane 12 is move the bladeforwardly of the plane of rotation, and which are utilized to decreasepropeller pitch. The present scheme utilizes a propeller geometry whichmakes maximum use of these forces.

In order more clearly to observe the operating forces present in andresulting from the arrangement of the blade, a three dimensional diagramis provided in Fig. 5 wherein the blade neutral axis 14 is at an angle 6to the retention bearing axis 10, and the retention bearing axis I6 isat an angle to a radius extending through the point e. The plane XZ is avertical fore and aft plane passing through the axis of rotation. The YZplane is the plane of rotation taken through the point e and lyingnormal to the axis of rotation. The plane X'Y' is a plane parallel tothe axis of rotation and normal to the other two, and passes through theblade neutral axis M at threequarters of the blade radius. This planeactually is a spherical segment but may be considered as as a planesince the various angles to be discussed are small and the assumption ofthe use of the plane introduces only negligible errors. Similarly', theeccentricity of the point e from the shaft axis being slight is alsodisregarded as introducing no noticeable error.

As previously noted the propeller is so com structed that the retentionbearing axis 10 intersects the blade neutral axis !4 at the point e. Theintersection of the retention bearing axis 10 at The intersection at T6and embracing the point 16 is a representation of the propeller bladecross-section. The point H so far as the plane I2 is concernedrepresents the center about which the blade section'and its center ofgravity 16 may rotate in a circular orbit 86, by reason of the angle 6between the bearing axis and the blade neutral axis. In virtue of theforward offset and of the offset in the direction of rotation of thebearing axis with respect to a radius such as the Z axis, this offsetbearing represented by the angle the angle may be resolved into aforward angular component 4; and a lateral angular componentkp in thedirection of rotation whereby the point H lies forward of the YZ planeand advanced rotationally with respect to the XZ plane. and '6 may beconstructed according to the requirements of the propeller, within arange of 3 to 15 degrees, and to attain objectives of this invention; 6'will be made somewhat greater than 1; and thereby, the circular locus 86of the blade section center of gravity 16 lies predominantly forward ofthe YZ plane but also overlaps rearwardly of the YZ plane as shown.

It is further noted that when the angle 6 is fairly small, the locus ofthe blade center of gravity may be maintained within the area embracedby the thrust bearing annulus 20 when projected upon the plane '12, Thisassures a bear- .ainglloading which;isreasonablmuniformrthrouehtoutperiphery.

EI1$1W111 .beseenthat the rbladezrsection center-50f igravity' 'lfilies1ina quadrantof the circle-.85 which lie ibehin'd theucircle,:center :H and rotationally in 'retard with respect to the directionofrotation. iBhemadiusmL-jfi :on'theplane '12 'makesran angle a relativeto fa line :11, :82".-W1'ii(ih is parallel to the Y axis. This angle ais nonnallysofithe order ref-4'5 (degrees. and varies either .sidezthereof rthrough {one -half of thetolerable operating pitch :range oflthe propeller blade. :Correspondingly, ;a tangent to :thescircle 86 atsthezpoint :16 zoria. chord iintersectin the circle;=8 6 at the.normaloperating ipitchlimits will liesinrtherange of degreeseto the :Yaxis.

With satpropeller blade and bearing system-designed v:s'o that :theblade section atakesan T'operatiingrposition as :shown andxwith theangleszdrandib relatively small, the bending moments 'upon theibladezproper are-minimized. The:sta'bilizing and which changing forcesupon the'blade, due. to;cen- .trifugal-iand aerodynamic effects,-iyield;pitch .insureasing :and decreasing. forces of itheisame order refmagnitude and may :likewise be maximum "in value- Bhe rblade attains anequilibriumrcondiition when the resultant R -.of centrifugal andaerodynamic .=forces in :the :plane 2 is a continuaition oftth 'line H,"15. .Rmay be resolvedintoa more. and aft :component EX and .a :lateralgeomponentiF'y. isince the momentarms .H, 82 and :1-6, .BQLareof-Tthesame order of magnitude and since theforces Fx g'and lF are essentially.of. the :same (order of magnitude, moments for increasing mitch andmoments tforidecreasing :piitch will be oi ithe :same order 'of:magnitude .to :provide high sensitivity for pitch increase zor:decrease, and icon'currently will provide stable equilibrium when itheamoments due to Fx and Fy are .zequal, 1130 atitain :a fixed pitchposition.

=Changes in the values .of FX (and zF will occur as aresultof the'changeinthe R. :M. andwthus centrifugal force, .a change in air speed orthrust, and a change in torque. In automatic propeller constructionsofthe prior art, -it -may be noted that the geometry .of the systems .issuch that pitch change forces and, reciprocally, the moment arms uponvwhich these forces act, are of widely divergent orders of magnitude,yielding low sensitivity and a low degree ofstability with respe'ct topropeller pitch change. It is believed that, in "the-present invention,theoptimum geometry for the system has been chosen to secure the bestpossible sensitivity and stability.

I liixamples of the mode and characteristics of operation of thepropeller under assumed conditions are cited as follows. If pitchequilibrium ,OCC'LlldWith an engine R. P; of 2200 and :an'a'ir "speed of160 miles per "hour, propeller pitch lmay be of the order of 13 degrees'as shown, under which conditions, the moments due to forces Fx and Fywould be equal and the resultant R acting upon the blade would comprisea continua.- tion of the radius H, 15. If the air speed were to slackento 40 miles per hour and propeller power were increased with aconsequent speed increase to 2400 R. P. M., conditions which would beappropriate at takeoff, the force R will shift forward or clockwise,whereby Fy will increase relative to FX imposing a moment upon theblade, rotating it forwardly around the circle 86 to a decreased pitchposition where the moments due to the forces Fx and F will againbalance. In the new position the blade still lies in the laggingrearward quadrant of the circle 86 and the forces 75 loss of sensitivityto adjust pitch on account of and imom'entearms' toiobtain balancedmoments.

are still .o'fzlthe zsame :order-zof magnitude. .iI-f enginepowermndiaircraft attitude be :changed to z'securefaiflightispeedzof:10011VL; PeflsatanR. EFL-M. xii 2000 which :e'on diti'onssmightfbedesired during a sustainedfflightipliase, ashigher propellerbla'de pitchangle would the called for -to :absorb .engine power and ito provide anappropriate angle o'f attack. Wiith the :new :conditions, IR would shiftrearwar'dlyiorzcounterclockwise,iandzFx vwould increase relative to xF-(thrust decreasing and P. M. increasing whereupon 'centr ifugal effectdominates) therebyiimposingiajmoment'upomthe blade to swing itrearwardly in the quadrant :in thecircle 86 te an --increased pitchposition until 'the mements dueito FX-and F bal'ance whereupon theresultant-.3 becomes a, continuation of the radius-11,16. From theabove-assumed examples, it should be-clear that the blade will respondin pitch-change to variatisns in R. P. M., air speed "and other-factors.

When a uniform phase- 0f operation is to :be maintained, the-propellerwill change itch to maintain constant R. P. if the transient changes incentrifugal or aerodynamic forces roccur on the propeller. For instance,a transient increase in a ir' speed permits 'higher R. P. M-. the l-iigherfi. *P. causes apitch increase to restoreR. P. -'M. to --normal.The speed regulation, which depends upon the sensitivity of the blade tounbalanced forces, is particularly good in this propeller because of theadvantageous geometry enabling relatively large pitch correcting mo--merits- =to be built up for a small deviation in pitch from that atwhichaerodynamic and centrifugal-forces balance. I In-case 'o'f enginefaflure in operation, the propeller R. P. M. decreases and the relativewind acts against the forward faces -'of the "blades to increase pitchtofeather them. A feathering stop-may be-pla ced- 'in 'the mm at apoint'to-yield a featheringblade pitch angle of anydes'ired value, suchas '75 degrees. The feathering-angle preferably should be flat enough toleave some windmilling torque on theengine for restarting it, but steepenough "so as not to cause undue drag. Astop isalso'placeddn the 'hub tolimit low pitch to fthatdes'irjed for takeofi, and desired, aselectivelyreleasable stop may be used to limit the high pitch angle .of thepropeller duringnorm'a'l powered flight. "In virtually all automaticpropellers ofthis {general type, the blades operate very close to thepia'ne of rotation due to the dominanceof centrifugal force overaerodynamic forces. The blade-*iszusually about 2 to 4 degrees ahead of.theplane o'flrotation. In this propeller, by designing it to have theconical locus of the blade overlap theplane of rotation by affewdegrees,. thelbladef's travel in its orbit, 'for normal operation,is controlled to the part of the rear, trailing quadrant of the conewhich lies at ap-' proximately 45 degrees to the plane of rotation. Thisis the part of the orbit, as previously inferred, where maximumeffectiveness for producing pitch changing moments is derived from boththe centrifugal and aerodynamic forces, respectively, for increasing anddecreasing pitch.

Without the proper relation of forward tilt 4m and angle 6, 6 beingslightly greater than x, as herein taught the stabilizing forces Fx andFy become very different in magnitude and concurrently, the moment armsthrough which these forces act become different, with a consequent*small changes in aerodynamic, centrifugal and other forces imposed uponthe propeller. In practice it may be found desirable to em- .ploycounterweights BU'to compensate for blade centrifugal twisting moment.However, since the normal'range of pitch variation in the propeller isof the order of about 8 degrees, the centrifugal twisting moment willvary slightly over such range. --reduce blade pitch toward zero may beovercome in this small range either by increasing forward Centrifugaltwisting moment tending to tilt of the thrust bearing axis '10 slightly,or by changing the angle of the blade chord with respect to the radiusH, 16.

Analytical evaluation of the propeller herein described is not coveredin this specification but it is known that both mathematical andgraphical a propeller organization may be cited wherein the propellerdiameter is of the order of 6', the blades are of wood and each weightabout 6 pounds. Such blades have a moment of inertia of about .2 slugfeet squared, a mounting center eccentricity e of 1", a blade center ofgravity located about 12" from such mounting center, a tilt angle 4m ofabout 7 degrees, anoflset angle 45y of about 3 degrees, and an angle ofabout 9 degrees. Such a propeller would be suitable for operation in therange of 2000 to 2400 R. P. M. on aircraft having a speed range of about40 to 100 miles per hour and on engines having power of the order of 75H. P.

v A larger and heavier blade made of metal would require a smallereccentricity e and the angles 41x, y and 6 would be decreased to obtaindesirable characteristics for larger engines and faster airplanes.

'As, will be clear from the foregoing, a relatively simple variableautomatic pitch propeller is provided by this invention, in which theblades readily respond to changes in air speed, engine power andpropeller speed to effect proper corresponding changes in pitch settingof the propeller blades. Further, the invention provides a system inwhich great stability is provided in pitch setting under conditionswhere no transient force changes exist. The mountings of the blades aresuch as to provide a minimum of resistance to the forces used formaintaining or. changing pitch setting in accordance with flightconditions. Thus, pitch changes are made gradually upon changes intransient conditions witha minimum of overswing and with a minimum oflag,

Though but a single embodimentillustrating the invention has beenillustrated and described,

it is to be understood that the invention may be applied in variousforms; Changes may be'made in the arrangements shown without departingfrom the spirit or scope of the invention as will a definition of thelimits of the invention.

What is claimed is:

1. In a variable pitch propeller comprising a hub, a socket on said hubfor the support of a blade, said socket containing a bearing having anaxis intersecting a hub radius in the plane of hub rotation at a pointspaced outwardly on said radius from the hub center, and said bearingaxis being sloped forwardly from said radius in the direction of flightand being sloped rotationally inadvance of said radius, the angle of thebearing axis with said radius being of the order of 5 to 15 degrees, ablade supported by said bearing and extendin outwardly from said hub,the neutral axis of said blade intersecting said hub radius at itsintersection with said bearing axis, the blade neutral axis being angledrelative to the bearing axis by an angle of the order of 5 to 15degrees, said blade being mounted for free swinging in said bearing in aconic path about said bearing axis, means to limit the free swinging ofsaid blade to an angular range of the order of 15 degrees betweenminimum and maximum pitch positions of the blade, said range being theoperating pitch range of the blade, said blade axis, when the blade isin a median pitch position, lying forward of the plane of rotation ofthe hub radius toward the direction of flight and lying in arotationally trailing position relative to said hub radius. r

2. A variable pitch propeller according to claim 1 wherein, in theoperating pitch range, a plane defined by said blade neutral axis andsaid hub radius makes an angle of substantially degrees with the planeof rotation of said hub radius.

' PAUL J. QUINN.

REFERENCES CITED The following references are of record in the 'file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,455,442 Leparmentier May 15,1923 1,872,337 Pillard Aug. 16, 1932 2,359,265 Hackethal Sept. 26, 19442,416,516 Everts Feb. 25, 1947 2,423,752 Biermann July 8, 1947 FOREIGNPATENTS Number Country Date 496,750 Great Britain Dec. 5, 1938 886,632France July 5, 1943

